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So yea, some people have expressed interest in just how the hell I do this. Here's a little guide. I'm leaving the pictures huge'ish for clarity.

Stuff you'll need:
Not pictured:
Soldering iron (duh). Having a nice skinny/pointy tip will help. I keep my Weller at max setting (850 degrees F) so it melts the solder quick with little contact time.
Magnifier of some sort to check your work.

Lets get started:

Take your FFC and snip it off at a nice point. If its your first time, leave some room for error as you'll likely screw up and have to snip it again:

Now, take the snipped FFC and scotch tape it down onto a hard surface:

We now need to scrape the thin plastic layer off the end of it, exposing the metal leads:
Pic of scraping tool I use:
Continue down the line and scrape the whole end of the FFC clean:

Readjust the FFC to a nice angle that you're comfortable with, re-tape it down and then use the exacto knife to split between the leads (this is the most precarious part of the whole deal IMO):

If you did a good job, you should have something that looks like this:

Cut a tiny rectangular piece of double sided tape out and apply it so that we can bend every other lead back and have the tape hold it in place:
Done:

Besides helping hold things in place, the double sided tape gives the FFC a bit more substance, so as when we touch it with our soldering iron tip it doesn't just shrivel up into a ball of goo. That being said, we'll apply a small rectangle of double sided tape to the remaining leads sticking out the end also:
Leave the paper on the opposite side of the double sided tape this time, we only need one side to be sticky here:
Done:

Now that's done we can prep our wires, Cut them to your desired length and tin the end of each one with a bit of solder (you only need a little bit, overkill here is bad):

Apply flux. Not too much, just enough to help aid in connecting:

Hold wire in place with tweezers, its important that the wire is pressed down hard against the FFC lead. Start at the end of the stripped wire and swipe your soldering iron forward to melt the solder and make the connection. This needs to be done quickly (as in like under a half of a second or so). If you take to long you will melt the FFC lead, plastic, metal and all:

Progress down the line:

Once done, test all your connections with a multimeter to make sure you have continuity between the end of the wire and the end of the FFC.

If all is well epoxy/hot glue that side of the FFC:

Rinse and repeat for the opposite side.

Its worth noting that I've been doing this a bit different lately, I've only been soldering to the leads needed for the actual data lines on the FFC. So pins: 1,3,5,7,9,11,13,15,17,19,21,22,23,24,25,26,27,28 and 29. So only 19 pins to solder.

I've then been connecting ground and 3.3v to the wiikey as so:

Hope this helps some people. I think this method is way better than using a breakout board.

Could have done with this when I attempted mine. I ended up breaking a few of the contacts by bending them back after I had soldered them so I gave up in the end and took the FPC connector from the DVD side of the wode and soldered the wires to that instead.

I'm 1/2 way through making one for myself, got past the hard bit of stripping and soldering down one side. I'm just waiting for my glue to dry since I couldn't find either hot glue nor epoxy around anymore at home - will post my results when it's all done.

Note for others: I used the cable from the Wii mainboard -> Wii DVD Drive and it needed the extra silver layer scraped off too but it came off just as easy as the white coating does.

Quick progress shots from my cable below. Note, I really recommend using the double sided table as Ashen recommends. I simply used a bit of thin cardboard and it does not give the tiny strands of metal any support so you have to be very careful when soldering on the wires that the flex doesn't move/tear.

Sorry for the crap quality, they're from a phone. one is without glue, one is after.

status update, I haven't finished a cable yet, I keep frying the other side .. I need a less powerful iron with a thinner tip it seems, but I'm going to keeping trying and get it done, there's plenty of room on the cable I've got to try at least another 3-4 times.

Ashen, I just noticed after I desoldered a GC DVD drive connector, if you bend back every second connection as you've done above on the flex cable, it perfectly lines up with half the pins on the GC DVD drive connector, I'm not sure if the pins match up correctly but it'd be pretty damn nice if they did!

The FFC that ships with the Wiikey Fusion are the ones I regularly use. They're all pretty much the same IMO.

You should be fine with any old soldering iron as long as you're good with it. I keep my weller @ 850 degrees F when I do this, that way it melts the solder on the pretinned wires quickly and I dont need alot of contact time.

just thought id mention when i did this to a 32 pin ffc. i found it was easier not to split the ffc up witha knife 1st..

Cut it n expose the contacts and so on..
tape the ffc down to a workable surface. put the tape just above the area you exposed your contacts. (I taped cardboard down to a table. then taped the ffc to that)
then flux up the ffc.
Tin your wire (i really reccomend labeling the wires 1st, and using kynar )

then solder to the 1st connection. when it sets gently lift the wire up. the ffc connection comes away from the rest of the ffc because of the previous heat..

you solder 1.. skip 1.. solder 1 skip 1.. untill you have done the 1st 16. glue those down.
then you can do the second set..

I found that easier and faster as it skips the cutting up step entierly. and if you arent to good with a knife, you may find some of the pads you cut up have more than 1 connection on them which means your going to have a bad time.